This invention relates to a graphite intercalation compound in the form of a film which is stable and elastic in nature and which is useful for utilization as a highly electrically conducting material, a superconducting material, an electric cell material, a chemical reagent, a catalyst for organic reactions, a gas storage and gas concentration material, a raw material for the production of expanded graphite, a lubricant, etc. The present invention is also concerned with a method of preparing such a graphite intercalation compound.
In graphite carbon atoms are arranged in planar layers each in the form of a regular hexagonal network. A graphite intercalation compound is a compound in which the carbon layers are intercalated or inserted with an intercalant such as molecules, ions or atoms. Graphite intercalation compounds are characterized by their variety of composition and structural and contain as their intercalants various chemical species including elements such as alkali metals and halogens and compounds such as organic halides, acids and ammonia. Even the same intercalant can give graphite intercalation compounds with different interposition structures (stage structures) or different compositions depending upon the reaction conditions under which the intercalation compounds are prepared. Graphite intercalation compounds may be broadly classified into two groups according to the type of interaction between the guest compound (intercalant) and the host graphite between the layers of which the guest is intercalated. The first group is of a type in which charge transfer occurs between the intercalant and graphite so that there is an electrostatic attractive force between them. The second group is of a type in which the intercalant and carbon atoms are bound covalently (covalent bond type). The charge transfer type graphite intercalation compounds may be further classified into a donor type in which the intercalant is an electron donor to the graphite layers and an acceptor type in which the intercalant is an electron acceptor
A number of proposals have been made for the utilization of intercalated graphite compounds because of their variety. For example, graphite intercalation compounds containing as intercalants AsF.sub.5, SbF.sub.5, HNO.sub.3, FeCl.sub.3, CuCl.sub.2, H.sub.2 SO.sub.4 and SO.sub.3.sup.- are proposed to be used as light weight, highly electrically conducting materials because of their electrical conductivity comparable to copper. There are proposals to use K-, Rb- and Cs-containing graphite intercalation compounds as superconducting materials, (CF).sub.n - and (C.sub.2 F).sub.n -containing graphite intercalation compounds as primary battery materials, K- and NiCl.sub.2 -containing graphite intercalation compounds as secondary battery materials and Br.sub.2 -containing intercalation compounds as temperature difference cells. Graphite intercalation compounds are also proposed to be used as reagents and catalyst for organic reactions and as materials for the storage and concentration of gases. For instance, intercalation compounds of K and Li are expected to be used as reagents for polymerization, those of Br.sub.2, SbCl.sub.5 and AsF.sub.5 as reagents for halogen-participating reactions, those of K and K-FeCl.sub.3 as catalysts for ammonia synthesis, those of H.sub.2 SO.sub.4 as reagents for esterification and those of K as hydrogen-storage of hydrogen-concentration materials. Additionally, graphite intercalation compounds having H.sub.2 SO.sub.4 and HNO.sub.3 are suggested to be used as a raw material for expand graphite, those having F as a lubricant and those having Fe, Co and Ni as a catalyst for diamond synthesis.
In spite of the various attractive properties of graphite intercaltion compounds, however, they are not actually utilized in practice at present except in only a few fields because of the following two fundamental problems involved therein.
The first problem in the conventional graphite intercalation compounds is difficulty of obtaining of suitable host graphite. In the preparation of a graphite intercalation compound, the degree of graphitization of the host graphite is one of the important parameters, i.e. a higher degree of graphitization is more preferable for the formation of intercalation compounds. Thus, natural graphite, Kish graphite or highly oriented, thermal cracking graphite, which has a high degree of graphitization, has been used for the preparation of intercalation compounds with excellent properties. However, such graphite is in the form of a block or minute lammelas and is very expensive. Since host graphite materials with both a high degree of graphitization and a large area like films are not available at present, graphite intercalation compounds of desired shape and properties are failed to be manufactured.
The second problem is related to the stability of graphite intercalation compounds. Namely known intercalation compounds are unstable and easily decomposed in air, though the degree of unstability varies with the type of the intercalant and with the degree of graphitization of the host graphite. A diversity of proposals have been made to improve the stability of graphite intercalation compounds, but they are still unsatisfactory.